A time series may be defined as a list of key figure values for consecutive time periods that is attached to a combination of parameter values (characteristics). The characteristics, the key figure name and the time period form a semantic key to identify a single key figure value. Such a time series may be the number of items sold per time interval. The time interval may be a day, a week, two months, etc. Parameters may be attached to the time series for characterizing the time series, for example denoting the store, or the item concerned.
Another example of time series are meteorological data useful for weather forecast. Yet another example is control and measurement data of a complex chemical production plant.
The simplest way of storing time series data in a data base table follows from the definition of the time series: the key is formed by the parameter values and the time period and an attribute stores the time series value.
A problem arises when a time series among a large amount of data is to be accessed in a data base. Then, a straight-forward storing of data relating to time series is no longer the method of favor.